1. Field of the Invention
This invention relates generally to magnets and magnet holders and, more specifically, to magnet and holder combinations having improved axial and rotational stability.
2. Background
Magnets have many uses in modern devices. Magnets are often used with sensors to detect the position of machine elements or to determine the speed, torque or direction of the movement of parts relative to each other. Such applications may be found in computers, printers and other electronic devices. Magnets also work with sensors in many automotive applications such as automatic brake systems. Magnet-sensor combinations also are an important part of smart remote actuators in automotive applications such as those that control air intake vents in turbochargers for diesel engines. Recently magnet-sensor combinations have been used extensively in electrically assisted power steering applications.
In most such applications the magnet is a bonded magnet that has been magnetized to have a pre-selected polarity. In many applications the magnet is supported and positioned during use by a magnet holder. In electronically assisted power steering applications, for example, such a magnet is retained by a holder on the end of a variable-speed motor shaft. The shaft spins the magnet-magnet holder assembly both clockwise and counter clockwise at speeds that can range up to 3,000 rpm or higher depending, for example, on the direction and speed the driver turns a vehicle's steering wheel. Sensors detect the steering wheel movement by detecting the speed and the direction of rotation of the magnet.
Rotational and axial stability of the magnet relative to the magnet holder is of great importance, especially when sensing of the magnet's rotation is used to control or to assist in steering an automobile. Sensing the speed and direction of a magnet's rotation typically involves sensing movement of the pre-determined polarity of the magnet as it rotates. Rotational slipping of the magnet in the magnet holder would cause the sensor to send incorrect information to a power assisted brake or to a steering mechanism. Likewise, axial movement of the magnet in the magnet holder, or axial separation of the magnet from the magnet holder, during operation would at least cause a sensor to send incorrect information to the controlled device and could prevent operation of the device.
There is a need for a magnet-holder assembly that provides improved axial and rotational stability of the magnet in the holder.